107 lines
3.2 KiB
Python
107 lines
3.2 KiB
Python
# Copyright (C) 2014 Nippon Telegraph and Telephone Corporation.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import weakref
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#
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# Internable
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#
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class Internable(object):
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"""Class that allows instances to be 'interned'. That is, given an
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instance of this class, one can obtain a canonical (interned)
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copy.
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This saves memory when there are likely to be many identical
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instances of the class -- users hold references to a single
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interned object instead of references to different objects that
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are identical.
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The interned version of a given instance is created on demand if
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necessary, and automatically cleaned up when nobody holds a
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reference to it.
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Instances of sub-classes must be usable as dictionary keys for
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Internable to work.
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"""
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_internable_stats = None
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_internable_dict = None
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def __init__(self):
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self._interned = False
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class Stats(object):
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def __init__(self):
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self.d = {}
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def incr(self, name):
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self.d[name] = self.d.get(name, 0) + 1
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def __repr__(self):
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return repr(self.d)
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def __str__(self):
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return str(self.d)
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@classmethod
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def _internable_init(cls):
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# Objects to be interned are held as keys in a dictionary that
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# only holds weak references to keys. As a result, when the
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# last reference to an interned object goes away, the object
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# will be removed from the dictionary.
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cls._internable_dict = weakref.WeakKeyDictionary()
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cls._internable_stats = Internable.Stats()
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@classmethod
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def intern_stats(cls):
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return cls._internable_stats
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def intern(self):
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"""Returns either itself or a canonical copy of itself."""
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# If this is an interned object, return it
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if hasattr(self, '_interned'):
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return self._internable_stats.incr('self')
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#
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# Got to find or create an interned object identical to this
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# one. Auto-initialize the class if need be.
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#
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cls = self.__class__
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if not cls._internable_dict:
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cls._internable_init()
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obj = cls._internable_dict.get(self)
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if (obj):
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# Found an interned copy.
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cls._internable_stats.incr('found')
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return obj
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# Create an interned copy. Take care to only keep a weak
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# reference to the object itself.
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def object_collected(obj):
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cls._internable_stats.incr('collected')
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# print("Object %s garbage collected" % obj)
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pass
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ref = weakref.ref(self, object_collected)
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cls._internable_dict[self] = ref
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self._interned = True
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cls._internable_stats.incr('inserted')
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return self
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